Traction battery cooling system with coolant proportional valve

ABSTRACT

A cooling system is provided for a traction battery of an electrified motor vehicle. That cooling system includes a cooling circuit, a refrigerant circuit, a plurality of flow control valves and a control system. That control system includes a controller configured to (a) control operation of the plurality of flow control valves, including a coolant proportional valve, and (b) prioritize cabin cooling over traction battery cooling.

TECHNICAL FIELD

This document relates generally to the motor vehicle equipment fieldand, more particularly, to a traction battery cooling system for anelectrified motor vehicle. That cooling system incorporates a coolantproportional valve and a refrigerant-to-coolant heat exchange chiller.

BACKGROUND

Hybrid electric vehicles and electric vehicles use an electric motor topropel the vehicle. The power is supplied to that electric motor by atraction battery. The traction battery is configured to store anelectrical charge and may also be used to power other vehiclecomponents. Efficient use of the battery may significantly extend therange of the motor vehicle. Since the battery power availability isaffected by battery temperature, hybrid and electric vehicles generallyinclude a liquid cooling system for the traction battery. Many suchsystems incorporate a refrigerant-to-coolant chiller that is coupled tothe vehicle cabin's cooling/heating, ventilation and air conditioning(HVAC) system. As a result, utilization of the chiller to providetraction battery cooling may lead to temperature swings of theconditioned air being discharged into the motor vehicle cabin. Suchswings in temperature may be noticeable by the vehicle occupants and,therefore, are not desired.

This document relates to a new and improved traction battery coolingsystem for an electrified motor vehicle that limits or substantiallyeliminates these temperature swings under normal operating conditionsthereby increasing vehicle occupant comfort and satisfaction.

SUMMARY

In accordance with the purposes and benefits described herein, atraction battery cooling system is provided for an electrified motorvehicle. That cooling system comprises a coolant circuit, a refrigerantcircuit, a plurality of flow control valves and a control system.

The coolant circuit circulates coolant between the traction battery andeither a battery radiator or a chiller. The coolant circuit alsoincludes a chiller bypass. The refrigerant circuit circulatesrefrigerant between a compressor, a condenser and either a firstevaporator or the chiller. The plurality of flow control valves areprovided in both the coolant circuit and the refrigerant circuit. Theplurality of flow control valves includes a coolant proportional valvein the coolant circuit between the traction battery and the chiller forcontrolling the flow of coolant through the chiller.

The control system includes a controller that is configured to (a)control operation of the plurality of flow control valves and (b)prioritize cabin cooling over traction battery cooling when the tractionbattery is at a normal or acceptable operating temperature.Advantageously, the cooling system functions to delay using the chillerfor battery cooling until the HVAC load for the motor vehicle cabin isstabilized and is below total AC capacity thereby reducing orsubstantially eliminating undesired swings in the conditioned air beingdischarged by the HVAC system into the motor vehicle cabin.

In some possible embodiments, the controller is configured to include afirst data input for ambient air temperature. Further, the controller isconfigured to include a second data input for HVAC blower speed. Inaddition, the controller is configured to include a third data input forevaporator temperature. In addition, the control system may furtherinclude an ambient temperature sensor and an evaporator temperaturesensor that are connected, respectively, to the first and third datainputs.

In some possible embodiments the plurality of flow control valvesincludes a battery coolant valve in the coolant circuit downstream ofthe traction battery and upstream of the battery radiator and thecoolant proportional valve. This valve controls the flow of coolant fromthe traction battery to either the battery radiator or the coolantproportional valve.

In some embodiments, the plurality of flow control valves includes athermal expansion device in the refrigerant circuit between thecondenser and the chiller for controlling flow of refrigerant into thechiller from the condenser.

In some possible embodiments, the controller includes a fourth datainput for traction battery temperature. In some embodiments, thecontroller includes a fifth data input for coolant temperature. In suchembodiments, the control system may further include a traction batterytemperature sensor and a coolant temperature sensor.

In accordance with yet another aspect, a method is provided forcontrolling traction battery cooling while limiting temperature swingsof conditioned air into a cabin of an electrified motor vehicle. Thatmethod includes the steps of (a) prioritizing, by a controller, cabincooling over traction battery cooling based upon HVAC load andevaporator error and (b) controlling flow of battery coolant to achiller by means of a coolant proportional valve under control of thecontroller.

Still further, that method may also comprise the steps of: (a)monitoring, by a first device, ambient air temperature, (b) monitoring,by a second device, HVAC blower speed, and (c) monitoring, by a thirddevice, evaporator temperature.

The method may further include the step of determining, by thecontroller, HVAC load based upon indicated HVAC blower speed andindicated ambient air temperature. In addition, the method may includethe steps of determining, by the controller, evaporator error bycomparing indicated evaporator temperature to a target evaporatortemperature and determining, by the controller, chiller AC capacity as afunction of evaporator error and HVAC load.

Still further, the method may include the step of monitoring, by afourth device, traction battery coolant temperature. Still further, themethod may include the step of calculating, by the controller, tractionbattery target coolant temperature based upon traction batterytemperature.

In addition, the method may also include other steps such ascontrolling, by the controller, the flow of coolant to the chiller basedupon indicated traction battery temperature versus traction batterytarget temperature.

Still further, the method may include the step of determining, by thecontroller, a maximum coolant proportional valve opening position as afunction of A/C chiller capacity. The valve opening position determinesthe coolant flow amount to the chiller. The method may also include thesteps of determining, by the controller, a coolant proportional valveopening target position as an output of a battery coolant temperatureProportional and Integral (PI) controller and determining, by thecontroller, a final coolant proportional valve opening position as afunction of the maximum coolant proportional valve opening position andthe coolant proportional valve opening target position.

The method may also include the steps of fully opening, by thecontroller, the coolant proportional valve to the chiller andcontrolling, by the controller, compressor speed based upon batterycoolant temperature error when operating in battery cooling only mode.

In the following description, there are shown and described severalpreferred embodiments of the cooling system and method of controllingtraction battery cooling while limiting temperature swings of theconditioned air being discharged into the cabin of an electrified motorvehicle. As it should be realized, the cooling system and method arecapable of other, different embodiments and their several details arecapable of modification in various, obvious aspects all withoutdeparting from the cooling system and method as set forth and describedin the following claims. Accordingly, the drawings and descriptionsshould be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated herein and forming a partof the specification, illustrate several aspects of the cooling systemand related method and together with the description serve to explaincertain principles thereof. In the drawing figures:

FIG. 1 is a schematic block diagram of the traction battery coolingsystem.

FIG. 2 is a schematic block diagram of the control system for thecooling system illustrated in FIG. 1.

FIG. 3 is a control logic flow diagram depicting operation of onepossible embodiment of the cooling system.

FIG. 3a is a detailed view of Box 92 of the control logic flow diagramdepicted in FIG. 3.

FIG. 4 is a table indicating HVAC load for one possible embodiment ofthe cooling system.

FIG. 5 is a table illustrating four different levels or states ofchiller operation management for one possible embodiment of the coolingsystem based upon load and evaporator error.

Reference will now be made in detail to the present preferredembodiments of the traction battery cooling system, examples of whichare illustrated in the accompanying drawing figures.

DETAILED DESCRIPTION

Reference is now made to FIG. 1 schematically illustrating the tractionbattery cooling system 10 adapted for an electrified motor vehicle suchas a hybrid electric vehicle or an electric vehicle. The cooling system10 includes a coolant circuit 12 for circulating a coolant between atraction battery 14 and either a battery radiator 15 and/or arefrigerant-to-coolant chiller 16 for heat exchange (there is no mixingof refrigerant and coolant). The coolant may be a conventional coolantmixture, such as water and ethylene glycol.

The traction battery cooling system 10 also includes a refrigerantcircuit generally designated by reference numeral 18. The refrigerantcircuit 18 circulates a refrigerant between an A/C compressor 20, an A/Ccondenser 22 and either or both of the two evaporators 24 ₁ or 24 ₂and/or the chiller 16. The refrigerant may be a conventionalrefrigerant, such as R134a or R1234yf.

As further illustrated in FIG. 1, the cooling system 10 also includes aplurality of flow control valves in the coolant circuit 12 and therefrigerant circuit 18. More specifically, the traction battery coolantvalve 26 is provided in the coolant circuit 12 downstream from thetraction battery 14 where it is adjusted to direct coolant flow througheither a first loop 30 between the traction battery 14 and the tractionbattery radiator 15 or a second loop 34 between the traction battery andthe chiller 16. A traction battery coolant pump 36 functions tocirculate the coolant through either or both loops depending upon theposition of the traction battery coolant valve 26. A sensor 33 monitorsthe temperature of that coolant upstream from the traction battery 14.

As still further illustrated in FIG. 1, the second loop 34 includes achiller bypass 35. Further, the plurality of flow control valvesincludes a coolant proportional valve 37 to direct coolant through thechiller 16 or around the chiller through the bypass 35 or both.

Referring to loop 18, the plurality of flow control valves also includesa front evaporator shutoff valve 38 between the condenser 22 and thefront evaporator 24 ₁, a rear evaporator shutoff valve 40 between thecondenser and the rear evaporator 24 ₂ and a refrigerant shutoff valve41 between the condenser and the chiller 16. In addition, a firstthermal expansion device 42 is provided in the refrigerant circuit 18between the front evaporator shutoff valve 38 and the front evaporator24 ₁. Similarly, a second thermal expansion device 44 is provided in therefrigerant circuit 18 between the rear evaporator shutoff valve 40 andthe rear evaporator 24 ₂. Further, a third thermal expansion device 46is provided in the refrigerant circuit 18 between the refrigerantshutoff valve 41 and the chiller 16. Here, it should be appreciated thatthe evaporator shutoff valve 38 and the first thermal expansion device42 could be combined into one device, if desired, to minimize possiblerefrigerant leak paths. The shutoff valve 40 and second thermalexpansion device 44 could be similarly combined as could the refrigerantshutoff valve 41 and the third thermal expansion device 46.

As illustrated in FIG. 2, the cooling system 10 also includes a controlsystem generally designated by reference numeral 50. As shown, thecontrol system 50 includes a controller 52. The controller 52 is acomputing device such as a dedicated microprocessor or electroniccontrol unit (ECU) operating in accordance with appropriate instructionsprovided by control software. Such a controller 52 may comprise one ormore processors, one or more memories and one or more network interfacesthat all communicate with each other over a communication bus.

The controller 52 is configured to (a) control operation of theplurality of flow control valves including, but not necessarily limitedto the traction battery cooling valve 26, the coolant proportional valve37 and the refrigerant shutoff valves 38, 40, and 41, and (b) prioritizecabin cooling over traction battery cooling when the traction battery isat a normal or acceptable operating temperature. Toward this end, thecontroller 52 is configured to include a first data input 54 that isconnected to a sensor or other device 56, such as another controller,providing data respecting the ambient air temperature. The controller 52is also configured to include a second data input 58 connected to asensor or other device 60, such as another controller, for providingdata input for HVAC blower speed.

As further shown, the controller 52 is also configured to include athird data input 62 that is connected to a sensor or device 64, such asanother controller, providing data respecting temperature of theevaporators 24 ₁, 24 ₂ (one sensor or device 64 per evaporator). Thecontroller 52 is also configured to include a fourth data input 66 thatis connected to a sensor or device 68, such as another controller,providing data respecting the traction battery coolant temperature.While not illustrated in FIG. 2, it should be appreciated that thecontroller 52 may include additional data inputs connected to othersensors or devices, including other controllers, that provide data inputrespecting other system operating parameters including, but notnecessarily limited to, refrigerant pressure (note sensor 21 in FIG. 1),traction battery temperature and cabin cooling requests from the HVACsystem of the motor vehicle.

Controller 52 is generally configured to provide the necessary coolingfor the traction battery 14 while utilizing a minimum amount of motorvehicle energy. Toward this end, the controller 52 is configured tooperate in three different battery cooling modes. In the first mode,which consumes the least amount of motor vehicle energy, the tractionbattery coolant valve 26 is positioned to circulate the coolant in thecoolant circuit 12 through the first loop 30 between the tractionbattery 14 and the battery radiator 15. Ambient air forced through theradiator 15 during motor vehicle movement functions to cool the coolantwhich is then circulated by the pump 36 back through the battery 14 inorder to maintain a desired operating temperature for the tractionbattery. In the event the temperature of the traction battery 14 risesto a certain predetermined temperature, the controller 52 operates in asecond cooling mode wherein the fan 74 is activated to force cooling airthrough the radiator 15 thereby providing additional cooling to thecoolant and the traction battery 14 through which the coolant iscirculated.

In the event the temperature of the traction battery 14 reaches apredetermined, higher temperature when operating in the second coolingmode, the controller 52 initiates a third cooling mode by repositioningthe traction battery coolant valve 26 to direct some or all of thecoolant through the second loop 34 so that the selected portion of thecoolant flow, as determined by the position of the coolant proportionalvalve 37, is pushed by the pump 36 to circulate between the battery 14and the chiller 16. It is in this mode that the controller 52 isconfigured to prioritize cabin cooling over traction battery coolingduring normal motor vehicle operation if the cabin is also being cooled.

Toward this end, a method of controlling traction battery cooling whilelimiting temperature swings of the conditioned air being discharged intothe cabin of an electrified motor vehicle is provided. That methodincludes the steps of (a) prioritizing, by the controller 52, cabincooling over traction battery cooling based upon HVAC load andevaporator error and (b) controlling flow of battery coolant to thechiller 16 by means of the coolant proportional valve 37. In addition,the method may further include the steps of: (a) monitoring, by a firstdevice 56, ambient air temperature, (b) monitoring, by a second device60, HVAC blower speed, and (c) monitoring, by a third device 64,evaporator temperature. The controller 52 then determines HVAC loadbased upon indicated HVAC blower speed and indicated ambienttemperature.

More specifically, as illustrated in FIG. 3, the algorithm determines ifbattery chiller capacity is available when the chiller 16 is requestedand thus determines how to control the coolant proportional valve 37. Ifthe chiller 16 is not available, it is assumed that the battery coolingwill continue via the radiator 15. The method starts at Box 76. Thefirst step is to determine if there is a chiller request (Box 78). Ifthe chiller 16 is not requested the algorithm goes back to the start. Ifthe chiller request is present, the controller 52 moves to Box 80 anddetermines/calculates evaporator error (Box 80) and HVAC load (Box 82).As illustrated in FIG. 4, HVAC load is a function of ambient airtemperature and HVAC blower speed and, therefore, is determined by thecontroller 52 based upon data provided by the sensors or devices 56, 60at the respective data inputs 54, 58. In the embodiment of the system 10illustrated in FIG. 4, an ambient temperature of 25 degrees C. and ablower speed percentage of 60% produces an HVAC load of 50.

Evaporator error is determined by comparing the actual evaporatortemperature as indicated by the sensor or device 64 at the third datainput 62 to a target evaporator temperature as stored in the controller52.

As illustrated in FIG. 3 the controller 52 then determines the chillerA/C capacity available for traction battery cooling (note Box 84) as afunction of the determined evaporator error and HVAC load. FIG. 5illustrates a function table for one particular embodiment of thecooling system 10. In this embodiment, an evaporator error of 3, 4 or 5indicates that the chiller 16 is not available for any level of tractionbattery cooling (Chiller Capacity State #0). In contrast, an evaporatorerror of 2 and a load of 30 indicates that the chiller 16 is availableat a minimum opening for battery cooling (Chiller Capacity State #1).Still further, an evaporator error of 0.5 and a load of 60 indicatesthat the chiller is available for reduced chiller cooling of thetraction battery 14 (Chiller Capacity State #2). Finally, for example,an evaporator error of 0 and a load of 50 indicates that a full level ofthe chiller 16 is available for traction battery cooling (ChillerCapacity State #3).

As illustrated in FIG. 3, if chiller A/C capacity is not available forcooling (Box 86), the operating algorithm returns to start. In thissituation, the battery thermal system will continue to cool via thebattery radiator 15 (with or without operation of the fan 74) andcontinue to request the chiller 16. Once chiller capacity becomesavailable, the battery thermal system will transition to the chiller 16.In other words, there are times when the battery cooling mode may berequesting the chiller 16 but still running in the battery radiator loop30.

In contrast, if evaporator chilling is available for the tractionbattery 14, the controller 52 translates the chiller AC capacityavailable to the appropriate maximum position of the coolantproportional valve 37 at Box 88. In the embodiment illustrated in FIG.3, when chiller capacity is indicated to be at a minimum, the controller52 may open the coolant proportional valve 37 in the coolant circuit 12to a maximum of 25% opening (Chiller Capacity State #1) to allow theflow of the coolant through the chiller 16 for heat exchange with therefrigerant in the refrigerant circuit 18 and cooling of the tractionbattery 14. In contrast, when the chiller 16 is available at the reducedlevel as determined in FIG. 5, the controller 52 calculates a maximumopening signal for the coolant proportional valve 37 50% (ChillerCapacity State #2) thereby allowing a maximum increase in the flow ofcoolant to the chiller 16 for heat exchange with the refrigerant andcooling of the traction battery 14.

When cabin and battery cooling are both required (Box 90 and Box 91),the closed loop valve position controller algorithm (Box 92) isinitiated. The algorithm to determine valve position is a closed loopcontrol algorithm that will open the coolant proportional valve 37 basedon battery coolant temperature. The previous step shown calculates amaximum valve opening based on chiller AC capacity. The valve will openin proportion to chiller capacity availability. Further, it should alsobe appreciated that the opening percentages indicated are presentedpurely for purposes of example and that the coolant proportional valve37 may provide for a full range of opening from 0% up to 100%.

Once the controller 52 determines the chiller capacity available(Chiller Capacity State #3), the coolant proportional valve 37 positionis determined by Box 92 (see FIGS. 3 and 3 a). Thus, the controller 52implements a battery coolant temperature PI controller (Box 94) tocontrol the coolant temperature into the traction battery 14. Thecoolant proportional valve 37 makes positional adjustments (Box 96)based upon the controller calculated battery coolant temperature error(Box 98) determined by comparing the actual or indicated battery coolanttemperature (Box 100) to the target battery coolant temperature (Box102) stored in the controller.

This PI control is always running in the controller 52, but chillercapacity states #1 and #2 apply the coolant proportional valve 37position max clip based on chiller A/C capacity (Box 104) which limitsthe coolant proportional valve 37 opening position (Box 106). Thecontroller 52 also controls the speed of the A/C compressor 20 basedupon evaporator error (Box 108). See FIG. 3.

In contrast, if the HVAC system is not in use for cabin cooling asdetermined at Box 90, the system 10 is operating in Battery Only Mode(Box 110). See FIG. 3. In this mode, the controller 52 fully opens thecoolant proportional valve 37 to the chiller 16 (Box 112) and controlsthe speed of the A/C compressor 20 based upon battery coolanttemperature error (Box 114).

Advantageously, the controller 52 has the ability to manage the flow ofcoolant to the chiller 16 at all times. This allows for traction batterycooling via the chiller 16 to be started smoothly and run continuouslywithout impact to the cabin. As a result, detrimental swings in thetemperature of the conditioned air passing through the evaporators 24 ₁,24 ₂ and later being discharged into the cabin are minimized. The system10 and related method prioritize cabin cooling by delaying the chillerstart and also provide a method to run at reduced chilling capacity tomaintain cabin comfort under changing A/C capacity conditions. Onlyunder extreme operating conditions where traction battery temperaturesrise to predetermined critical levels does the controller 52 prioritizebattery cooling over cabin cooling by first providing full AC capacityto the chiller 16 for traction battery cooling and any remaining ACcapacity to the cabin.

The foregoing has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theembodiments to the precise form disclosed. Obvious modifications andvariations are possible in light of the above teachings. All suchmodifications and variations are within the scope of the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

What is claimed:
 1. A cooling system for an electrified motor vehicle,comprising: a coolant circuit circulating coolant between a tractionbattery and either a battery radiator or a chiller; a refrigerantcircuit circulating refrigerant between a compressor, a condenser andeither a first evaporator or said chiller; a plurality of flow controlvalves in said coolant circuit and said refrigerant circuit; and acontrol system including a controller configured to (a) controloperation of said plurality of flow control valves and (b) prioritizecabin cooling over traction battery cooling when the traction battery isat a normal operating temperature; wherein, said coolant circuit furtherincludes a coolant bypass and said plurality of flow control valvesincludes a coolant proportional valve in said coolant circuit betweensaid traction battery and said chiller controlling flow of said coolantthrough said chiller.
 2. The cooling system of claim 1, wherein saidcontroller is configured to include a first data input for ambient airtemperature.
 3. The cooling system of claim 2, wherein said controlleris configured to include a second data input for HVAC blower speed. 4.The cooling system of claim 3, wherein said controller is configured toinclude a third data input for evaporator temperature.
 5. The coolingsystem of claim 4, wherein said control system further includes anambient temperature sensor and an evaporator temperature sensor.
 6. Thecooling system of claim 5, wherein said plurality of flow control valvesincludes a battery coolant valve in said coolant circuit downstream ofsaid traction battery and upstream of (a) said battery radiator and (b)said coolant proportional valve controlling flow of said coolant fromsaid traction battery to either said battery radiator or said coolantproportional valve.
 7. The cooling system of claim 6, wherein saidplurality of flow control valves includes a thermal expansion device insaid refrigerant circuit between said condenser and said chillercontrolling flow of said refrigerant into said chiller from saidcondenser.
 8. The cooling system of claim 7, wherein said controller isconfigured to include a fourth data input for traction batterytemperature.
 9. The cooling system of claim 8, wherein said controlleris configured to include a fifth data input for coolant temperature. 10.The cooling system of claim 9, wherein said control system furtherincludes a traction battery temperature sensor and a coolant temperaturesensor.
 11. A method of controlling traction battery cooling whilelimiting temperature swings of conditioned air into a cabin of anelectrified motor vehicle, comprising: prioritizing, by a controller,cabin cooling over traction battery cooling based upon HVAC load andevaporator error; controlling flow of battery coolant to a chiller bymeans of a coolant proportional valve under control of said controlled;determining, by said controller, a coolant proportional valve openingtarget position as an output of a battery coolant temperature PIcontroller; and determining, by said controller, a final coolantproportional valve opening position as a function of said maximumcoolant proportional valve opening position and said coolantproportional valve opening target position.
 12. The method of claim 11,further including: monitoring, by a first device, ambient airtemperature; monitoring, by a second device, HVAC blower speed;monitoring, by a third device, evaporator temperature.
 13. The method ofclaim 12, including determining, by said controller, HVAC load basedupon indicated HVAC blower speed and indicated ambient air temperature.14. The method of claim 13, further including (a) determining, by saidcontroller, evaporator error by comparing indicated evaporatortemperature to a target evaporator temperature and (b) determining, bysaid controller, chiller A/C capacity as a function of evaporator errorand HVAC load.
 15. The method of claim 14, further including monitoring,by a fourth device, traction battery temperature.
 16. The method ofclaim 15, including calculating, by said controller, traction batterytarget coolant temperature based on battery temperature.
 17. The methodof claim 16, further including controlling, by said controller, flow ofcoolant to said chiller based upon indicated traction batterytemperature versus target traction battery temperature.
 18. The methodof claim 17, further including determining, by said controller, amaximum coolant proportional valve opening position as a function ofsaid chiller A/C capacity.
 19. A method of claim 11, further includingfully opening, by said controller, said coolant proportional valve tosaid chiller and controlling, by said controller, compressor speed basedupon battery coolant temperature error when operating in battery onlymode.